(1) Field of the Invention
The present invention relates to a system and method for electronically controlling an engine operation having a safe function. The present invention relates specifically to the system and method for electronically controlling an opening angle of an engine throttle valve in accordance with operating variables of an accelerator and of a vehicle speed automatically controlling system. More specifically, the present invention relates to the system and method therefor in which a maximum opening angle of the throttle valve is limited so as to prevent an acceleration of the vehicle carried out against an intention of the vehicle driver and which is capable of utilizing the automatic vehicle speed controlling system in the vehicle.
(2) Background of the Art
Various types of the systems for electronically controlling an opening angle of the throttle valve of the vehicular engine in accordance with an operation of an accelerator have already been proposed.
Japanese Patent Applications Unexamined (first) Publications sho 61-46725 published on Mar. 7, 1986, 61-247829 published on Nov. 5, 1986, 61-247830 published on Nov. 5, 1986, 61-247831 published on Nov. 5, 1986 exemplify the previously proposed systems described above. In addition, a Japanese Patent Application Examined (second) Publication sho 51-31915 published on Sept. 9, 1976 exemplifies another one of the previously proposed systems described above.
In the previously proposed systems disclosed in the above-identified Japanese Patent Application Publications, the accelerator and engine throttle valve are not mechanically linked with each other. Then, when an operating variable (an angular displacement) of the accelerator is detected, a throttle actuator constituted by a reversible motor actuates the throttle valve to open or close in accordance with the detected operating variable of the accelerator.
Furthermore, if a failure occurs in a control system installed between the accelerator and the throttle valve, a limiter is installed which limits a maximum opening angle of the throttle valve in a mechanical cooperation with the accelerator so that the throttle valve can be closed in response to a release operation of the accelerator without failure, thus inhibiting an actuation of the throttle valve to open more widely exceeding the limited opening angle. Such a system with the inhibiting function as described above is exemplified by a Japanese Patent Application Unexamined (first) Publication sho 59-190440 published on Oct. 29, 1984.
In the system disclosed in the above-identified Japanese Patent Application Publication sho 59-190440, since the limiter which mechanically cooperates with the accelerator permits the maximum opening angle of the throttle valve to be limited at its opening angle, the throttle valve can be operated forcibly in its closed direction through the accelerator operation by the vehicle driver. Thus, an ensured closure of the throttle valve can be achieved.
However, since in the previously proposed system disclosed in the Japanese Patent Application Publication sho 59-190440 the maximum opening angle of the throttle valve can compulsively be determined only according to the angular displacement of the accelerator, the vehicle in which the previously proposed electronic engine operation system is mounted cannot apply such a system for automatically controlling a vehicle speed to a desired cruising speed without operation of the accelerator thereto. Hence, it is difficult to add the vehicle speed controlling function to the engine operation controlling system of the vehicle.